1. Field of the Invention
This invention relates to graphic plotter recording media. Particularly, this invention relates to transparent plotter sheet material.
2. Description of the Prior Art
Polymeric sheet materials have been extensively used as image receiving surfaces for use with overhead projectors or the like. However, a continuing problem with the use of polymeric transparencies has been the generally hydrophobic nature of these materials. Associated with the surface characteristics of the film are numerous problems including, for example, ink repulsion (e.g., hydrophobic films will cause hydrophilic inks to bead up on the surface rather than be absorbed) and low ink dry times for those that do absorb, smudging, color intensity, ink spreading etc.
An important use for polymeric transparency recording media substrates is with computer driven graphic pen plotters. These plotters use pens which trace across the recording medium surface. In multi-color plotters often numerous pen types are used. The pen types are purchased with the plotters or separately for special applications. Many of such pens are hard pointed which require a plotter substrate with integrity to avoid tearing, pen clogging and related problems. Generally, all the pens typically require low volatility inks to maintain the ink flow, in that the plotters work in an open environment. Low volatility inks exaggerate the problems of sorption and poor drying. Suggested solutions, such as coating silica on transparencies, increase sorption of inks but are abrasive and decrease normal pen life.
One proposed solution to the above problem involves coating the polymeric films with absorbent particles such as silica, coupled with employing a separate oil-based or hydrophobic ink with the particle coated transparency. However, in normal operations, pen plotters and like recorders utilize hydrophilic inks and ink pens. Consequentially, using coated transparent films which are designed to absorb hydrophobic inks require a troublesome pen and ink switchover. Obviously, it would be desirable in terms of efficiency, cost, and marketability if transparencies could be recorded by the same pen and ink arrangements used for opaque, e.g., paper, substrates.
A proposed solution to these problems is in U.S. Pat. No. 4,301,195, which discloses a polyester transparent sheet coated with two polymers, which are either used together in a single layer or separately as two layers. The first polymer is described as an epoxidized diene-containing material (e.g., cis-1,4-polybutadiene rubber epoxidized then aminized with a secondary monoamine such as dimethyl amine) and a polyvinyl alcohol-polyvinyl acetate resin (PVA). In the two layer construction the PVA is the upper or surface layer. A related U.S. Pat. No. 4,379,804, proposes a two layer system with a liquid permeable layer overlying a liquid sorbent layer. Exemplary liquid sorbent underlayers include polyvinyl acetate and gelatin, among others, and exemplary liquid permeable upper layers comprise cellulose acetate/butyrate or gelatin (of a different molecular weight), among others. Although these sheets allegedly have dry times less than 3 seconds, the search goes on for transparent sheets with greater color intensity, less abrasiveness, greater ink permeability, improved dry times, improved smudging resistance, lower costs, among other properties.
It is a general object of the present invention to provide a transparent film to solve or substantially alleviate the above noted problems in the art.
It is a more specific object of the present invention to provide a transparent film that is receptive to hydrophilic inks while maintaining sufficient surface integrity to be used with, e.g., plotter pens.
It is another object of the present invention to provide a transparent film which is relatively non-abrasive, thereby improving pen life.
It is another object of the invention to provide a coated pen plotter transparency that is easily produced and is absorbent to hydrophilic inks to produce sharp images with low-dry times and generally improved imaging properties.
These and other objects, as well as the scope, nature and utilization of the invention, will be apparent to those skilled in the art from the following description, and the appended claims.